18F is the isotope of choice for many PET cancer imaging applications.
PET imaging agents are often based on a labeled biomolecule. Examples include fluorodeoxyglucose (FDG); Octreotate, an octapeptide that is used to image cancer; and folate, which has been used to image cancer. Since the high energy particle bombardment used to produce 18F destroys complex organic molecules, 18F is first made as fluoride ion in a cyclotron and subsequently attached to the biomolecule used as the imaging agent. Also, conditions used to incorporate 18F are often too harsh for direct labeling of many biomolecules. Therefore, 18F is usually introduced into a precursor (such as an aryl fluoride) that is then subsequently appended to a larger molecule. Such multi-step procedures result in delays, with consequent loss in specific radioactivity.
Some methodologies for incorporating 18F into imaging agents have been reported, including a new approach which makes use of boron as an acceptor capable of binding several 18F atoms, thus increasing the density of positron emitters in the resulting imaging agent (see, for example, PCT publication WO 2005/0077967). In addition, the use of arylboronic acids/esters as 18F acceptors has been reported. This approach has circumvented the previous practice of generating aryl fluorides in multi-step procedures. 18F radiolabeled substituted aryl-fluoroborates for use in PET imaging have also been reported (see, for example, WO 2009/012596).